Polymer actuators or electroactive polymers (EAP) offer the unique possibility to generate thin-film actuating surfaces. This can be used for many different applications, such as, for example, controllable optical elements, so-called electronic muscles, and applications where a controllable surface topography is used to modify the appearance and/or tactile properties of a surface.
Polymer actuators typically comprise a dielectric elastomeric film sandwiched between two deformable electrodes. When a voltage is applied between the electrodes, an electrostatic force is generated that strives to push the electrodes closer to each other. When this happens, the portion of the dielectric elastomeric film between the electrodes is compressed until the compression force balances the electrostatic force, at which point the dielectric elastomeric film has (at least locally) become thinner. Due to the incompressibility of the dielectric elastomeric film, a local thickness reduction translates to a change in another dimension of the polymer actuator. By properly selecting electrode geometry and controlling the voltage applied between the electrodes, the surface topography of the polymer actuator can be controlled by applying the between the electrodes. The control of the surface topography is, however, limited by the properties of the dielectric elastomeric film and the configuration of the electrodes.
In order to expand the controllable range, at least in terms of amplitude, US-2008/0289952 discloses to provide a passive layer on top of one or both sides of a stack formed by the dielectric elastomeric film and control electrodes. The passive layer is softer than the dielectric elastomeric film in order to amplify out-of-plane deformations and create more visible surface features.
Although providing for an increased range of control for out-of-plane deformation, the polymer actuator according to US-2008/0289952 is still limited to controlling the locations of the deformations through the electrode geometry, which may make it difficult and/or complicated to achieve certain surface topographies.